The intensive use of antibiotics has exerted a selective evolutionary pressure on microorganisms to produce genetically based resistance mechanisms. Modern medicine and socio-economic behaviour exacerbate the problem of resistance development by creating slow growth situations for pathogenic microbes, e.g. in artificial joints, and by supporting long-term host reservoirs, e.g. in immuno-compromised patients.
In hospital settings, an increasing number of strains of Staphylococcus aureus, Streptococcus pneumonia, Enterococcus spp., and Pseudomonas aeruginosa, major sources of infections, are becoming multi-drug resistant and therefore difficult if not impossible to treat:                S. aureus is β-lactam, quinolone and now even vancomycin resistant;        S. pneumoniae is becoming resistant to penicillin, quinolone and even to new macrolides;        Enteroccocci are quinolone and vancomycin resistant and β-lactams were never efficacious against these strains.        
Further new emerging organisms like Acinetobacter spp. or C. difficile, which have been selected during therapy with the currently used antibiotics, are becoming a real problem in hospital settings.
In addition, microorganisms that are causing persistent infections are increasingly being recognized as causative agents or cofactors of severe chronic diseases like peptic ulcers or heart diseases.
In a chimeric molecule two or more molecules that exist separately in their native state are joined together to form a single entity (i.e. molecule) having the desired functionality of all of its constituent molecules.
Molecules wherein two antibiotics that have two different modes of action have been linked have been reported in the literature (e.g. Journal of Antimicrobial Chemotherapy (1994), 33, 197-200). Many of them are however such that the two antibiotic parts are released after biological activation (e.g. central ester cleavage, beta-lactam cleavage). Chemically and biochemically stable chimeric molecules that bind, as such, in two different targets have been more seldom reported. For example, oxazolidinone-quinolone hybrids have been reported as useful antimicrobial agents effective against a variety of multi-drug resistant pathogens (WO 03/032962, WO 03/031443 and WO 2004/096221, WO 2005/023801 and WO 2005/058888). Further, synthesis and biological evaluation of these hybrids (Bioorg. & Med. Chem. (2003), 11, 2313-2319) and the influence of the central spacer on the antibacterial activity in the structure-activity relationship in the oxazolidinone-quinolone series have also been reported (Bioorg. Med. Chem. Lett. (2003), 13, 4229-4233). All these derivatives contain a 4-aminomethyl-oxazolidinone rest as part of the oxazolidinone pharmacophore.